Hi Tracey
It's our 4th time in Lanzarote and will be the third time we've been in March (but first time with our baby) It is usually around mid twenties and clear skies, the island is much greener early on in the year too, the sea is quite cool though so you'll have to be brave if you intend to have more than a paddle!
We go on 5th March, and are staying in Puerto Del Carmen Old Town, love it there

Where are you staying??